In a growth area for grass, such as a golf course, a lawn, grassplot in a park and the like, the grass present in a passage where people walk by or in a traffic line where a vehicle such as a cart in a golf course and the like passes through is repeatedly trampled down and damaged, and therefore renovation of grass is a considerable expense.
Accordingly, a grass protection mat is constructed to prevent damage of grass by distributing a load even when the grass is trampled down by people or vehicles in such a grass growth area, e.g. a traffic line area via which the people or vehicles move.
So far, a conventional known grass protection mat has been disclosed to roughly include a body forming a frame of the mat, a rug supported on the ground, a protruding pillar supporting a load, a buffering wing distributing the load, and an outer frame maintaining an outer frame of the mat.
Further, the outer frame may be provided with a hook means for connecting the mats, and an opening for coupling with the hook means of the adjacent mat. Alternatively, a bent hook may be provided in the outer frame and fitted to the outer frame of the adjacent mat to thereby connect the mats.
In case of the known grass protection mat, the mats to be constructed on the ground are connected by the hook means and the opening or by the bent hook, so that the outer frames of the mats are in close contact with each other.
Most of known grass protection mats are molded with a synthetic resin having elasticity, and therefore the mats being in close contact with each other after the construction are expanded or contracted in accordance with change in temperature.
Particularly, in summer, the mat constructed on the ground is directly exposed to sunlight and is thus likely to be terribly expanded. On the other hand, in winter, the mat constructed on the ground is likely to be contracted. In this regard, the mats are required to be in close contact with each other regardless of the ground and seasons (high or low temperature). When the mats are not harmonized with the ground, the mats are curved or moved like waves.
When the conventional grass protection mats are connected, the outer frames of the mats are in close contact with each other, and it is impossible to compensate for the expansion of the mats. Therefore, the contact portions between the mats such as the close-contact outer frames of the mats are likely to be excessively uplifted from the ground. Such uplift of the mats has been frequently problematic.
On the other hand, when the mats with the close-contact outer frames are contracted, the bodies or outer frames of the mats are pulled and it is likely to disconnect some portions of the mats.
To solve such a problem, there has been proposed a conventional grass protection mat, in which a contraction-expansion compensatory connector is used to assemble four small mat units into the grass protection mat, and the outermost outer frames of the mat are connected to other mats, thereby guiding the mats to move to compensate for the contraction and the expansion of the mat and preventing the mats from uplifting from the ground or being disconnected.
However, the above-mentioned grass protection mat, in which a plurality of mat units are connected using a predetermined compensatory connection means to compensate for the contraction-expansion of the mat units has problems that its configuration is complicated, the need of additional materials causes production to be difficult, a production cost increases, and a grass passing space becomes narrower because of the presence of the outer frame. Further, the narrow grass passing space makes a photosynthesis space be insufficient.
Further, when the outer frames of the mats are connected using the contraction-expansion compensatory connection means, an efficiency of compensating for the contraction-expansion of the mats is insufficient.